Fluorinated alkanes are used as gases for plasma reactions, fluorine-containing intermediates of medicines, and media such as cooling/heating media. In particular, highly-purified fluorinated alkanes are suitably used as plasma etching gases, gases for the chemical vapor deposition method (CVD) and the like in the field of the production of semiconductor devices using plasma reactions.
As a method for producing a fluorinated alkane, there has hitherto been known a method in which an alkylsulfonyl fluoride is allowed to react as a fluorinating agent with a corresponding alcohol.
For example, Non Patent Literature 1 describes an example of the fluorination of the hydroxyl group in a steroid precursor by using, in a toluene solvent, a perfluorobutanesulfonyl fluoride as a fluorinating agent and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base.
Non Patent Literature 2 describes a method for fluorinating primary to tertiary alcohols, in a tetrahydrofuran or methylene chloride solvent, by using a ternary system of perfluorobutanesulfonyl fluoride-a trialkylamine-hydrogen fluoride complex-a trialkylamine.
Non Patent Literature 3 describes an example of the fluorination of various alcohols by using nonafluorobutanesulfonyl fluoride as a fluorinating agent, and DBU as a base.
Patent Literature 1 describes a fluorination of a high molecular weight alcohol compound, in a solvent such as toluene or diethylene glycol dimethyl ether, by using a fluoroaliphatic sulfonyl fluoride as a fluorinating agent, and DBU as a base.
Patent Literature 2 also describes a fluorination of an aliphatic alcohol, an aromatic hydrocarbon compound and an enol compound, in an inert organic solvent such as toluene, by using nonafluorobutanesulfonyl fluoride as a fluorinating agent, and an amidine base as a base.
However, the fluorinating agent used in these documents, namely, the perfluoroalkanesulfonyl fluoride is expensive, and thus not appropriate to industrial use. The perfluoroalkanesulfonic acid derivatives produced in the case where these fluorinating agents are used also suffer from an apprehension of long-term toxicity and a safety problem.
These documents also describe only the examples using alcohols relatively high in boiling temperature and complicated in structure as raw material alcohols; thus, when alcohols having 3 to 5 carbon atoms are used as raw materials, the possibility of the production of fluorinated alkanes having 3 to 5 carbon atoms is not clear.
On the other hand, the following methods are known as methods for producing fluorinated alkanes having 3 to 5 carbon atoms.
Patent Literature 3 describes a production of 2-fluorobutane at a yield of 46%, by bringing N,N′-diethyl-3-oxo-methyltrifluoropropyl amine as a fluorinating agent into contact with 2-butanol.
However, the N,N′-diethyl-3-oxo-methyltrifluoropropyl amine used may deserve to be referred to as an extremely expensive fluorinating agent because of being produced from 4-chloro-3,4,4-trifluoro-2-butanone, industrially difficult to obtain, and two equivalents of diethylamine. In addition, the yield of the target product, 2-fluorobutane, of 46% is not satisfactory.
Patent Literature 4 describes a production of 2-fluorobutane at a yield of 68% from 2-butanol by using triethylammonium hexafluorocyclobutane as a fluorinating agent in the absence of a solvent.
However, the triethylammonium hexafluorocyclobutane used is a product produced by using hexafluorocyclobutene industrially extremely expensive and strongly toxic.
Patent Literature 5 describes a production of fluorinated sec-butyl by bringing sulfur hexafluoride into contact with a sec-butyl lithium cyclohexane-hexane solution.
However, the sec-butyl lithium cyclohexane-hexane solution used is high in ignitability to offer a problem with respect to handling. In addition, sulfur hexafluoride has an extremely long atmospheric lifetime, resulting in a problem of safety.
Moreover, Patent Literature 6 describes a production of 2-fluorobutane by hydrogenating 2-fluorobutadiene in the presence of a catalyst.
However, the method described in this document encounters a problem that 2-fluorobutadiene, the raw material, is difficult to obtain.
As described above, the methods described in these documents are not capable of being said as favorable industrial production methods of fluorinated alkanes.
In these documents, there are no descriptions on, e.g., the method for treating or the method for recovering the sulfonate complex of the amidine base by-produced by using perfluorosulfonyl fluoride as a fluorinating agent and by using an amidine base as a base.
On the other hand, Patent Literature 7 describes a method of recovering, by adsorption with activated carbon, tetramethylpropane diamine contained in waste water as a method for recovering a water-soluble amine.
Patent Literature 8 also describes a method for recovering an amine as follows: the amine in waste water is adsorbed on a cation exchange resin, then desorbed from the cation exchange resin by using an alkaline solution as an eluent, and the eluate is concentrated to recover the amine.
However, these documents describe the recovering of the amine from waste water with an adsorbent, in consideration of the reduction of environmental effect and load, but do not describe the handling of the recovered amine.
The amidine base such as DBU is a base extremely expensive for industrial use, and the amidine base is desired to be recovered and reused as much as possible from the viewpoint of the cost reduction.